Method of producing cellulose



Patented Oct. 20, 1931 PATENT OFFICE BROR NATANAEL SEGERFIET, OF BOHKISGH KRUIMIAU, CZECHOSLOVAKIA METHOD OF PRODUCING CELLULdSE Ho Drawing. Application filed April 21, 1928 Serial No. 271,985, and. in Sweden April 23, 1927.

In the production of cellulose by boiling cellulosic substances with acid or alkaline digester liquor; and afterwards washlng the cellulose obtained in diflusers or similar washing apparatus, it has hitherto been common practice to use the strongest waste or black-liquor obtained from-the difiusers or other washing apparatus for the regeneration of fresh digester liquor or white liquor and consequently, there only remained waste liquor of a weaker concentration available forthe-purpose of adding to the white liquor in order to make up the required volumeof total liquor in the digester. The washing of the pulp in the difli'users was performed 1n such manner that the waste liquor drawn from one diffuser-being washed with hot water, was not passedover to the top of a second newly blown'difi'user to serve as a primary o wash in thesame, until the concentration of the waste liquor from the first difiuser had decreased to a specific gravit of 1.074, or

even lower. By using a wea black liquor to make up the required volume of total liqnor in the digester and as a primary wash in a newly blown difi'user the black liquor obtained from such difiuser for the regeneration of white'liquor will only have a concentration not exceeding 1.107, and consequently,

large quantities of water must be evaporated from the same. 'The regenerated soda has as ,a rule been dissolved in molten state in water or in a weak NaOH-solution, but since the degreeof causticizing decreases at a high concentration of the sgda soluton, it is common practice not to make the soda solution of a higher concentration than of a specific gravity of 1.179, and therefore, when such soda solution is causticized, the White liquor 40 obtained will have a low concentration, and

this liquor when used in the digester will give a weak black liquor. I

The present invention has for its purpose to render it possible to obtain from the diffusers, or other washing apparatus, a waste liquor of a higher concentration than that hitherto obtained, so that the volume of black washing apparatus used, is utilized as suplemental 1i uor added to the fresh white iquor to ma e up the required volume of total liquor for a subsequent cook. From this cook a waste liquor will thus be obtained which has a higher concentration than usual, and the strong waste liquor first drawn from the diffusers from this cook is used as supple mental liquor for the next cook. By proceeding in this manner practically any desired concentration of the waste liquor may beobtained. The waste liquor used as supplemental liquor should have a specific gravity of at least 1.124. A further feature of the present method consists in that as a primary wash in a newly blown difi'user waste liquor -drawn from another difi'user is used which,

when such washing is begun, has a comparativel high concentration, namely, a specific gravity of at least 1.090, whereby the waste iquor passing from such newly blown diffuser will be less diluted.

A further feature of the present method, as applied to the use of alkaline digester liquor, consists in that the soda obtained by the regeneration of the waste liquor, is dissolved ,in a strong NaOH-solution holding at least 50 kg. NaOI-I per cu. m., whereby it is possible to Increase the concentration of the resulting solut1on,1. e., the green liquor, sincethe same quantity of sodium carbonate may be dissolved as when water or a weak NaOH-solu- 5 tion is used, without the quantity of lime to be added for causticizing having to be increased. The white liquor thus prepared will therefore contain more NaOH per cubic meter than is now usual, and consequently, a less volume of water for the total active alkali used per charge. Therefore, a correspondingly greater volume of strong black liquor obtained in the manner above stated, can be 5 added to the white liquor to make up the required .volume of total liquor, which will aid to give a high concentration of the waste liquor resulting from the cook.

In order to make the present method more easily understood, a manner in which it may be carried out in practice will now be described.

A vertical digester for sulphate cellulose is charged with 10000 kg. wood chips, holding2500 kg. water, after which fresh digester liquor, termed white liquor here below, is added, said liquorbeing assumed to have a specific gravity of 1.142 and consisting of NaOI-I, Na s and some Na CO in such quantities that the active alkali, i. e. NaOH and Na s, amounts to 1400 kg. Assuming that the strength of the white liquor is 120 kg. active alkali per cu. m., 11.7 cu. m. white liquor is thus required. This quantity of liquor is too small, however,'to effect the circulation required for the digestion, and for this reason waste liquor from a preceding digestion, termed black liquor here below, must be added. In this case 13.9 cu. m. of such'black liquor having an assumed specific gravity of 1.107, are added. The total quantity of liquor, including the water in the wood, thus becomes 28.1 cu. m.

Now, the invention has for its purpose by various steps in the process of manufacture to concentrate the black liquor obtained from the digester and which is to be regenerated. One step consists in removing water from the digester liquor during the digestion, either by means of powerful gassing off, r by evaporation of the digester liquor in special apparatus connected to the digester. By gassing 011? it should be possible, in the present case, to remove 1200 kg. water from the digester. In the remaining digester liquor lignin etc. is dissolved from the wood during the digestion, so that, in the case assumed, the black liquor may be assumed to have a specific gravity of 1.149 at the end of the digestion. When 50 the digestion is finished, the pulp and the black liquor are blown at a pressure of from 3 to 4 kg. from the digester to a difiusor, or

similar washing apparatus, in order to wash the cellulose obtained clear from the black 66 liquor. A newly blown diffusor is first washed with a weak liquor from another previously blown difiusor, whereby the strong black liquor in the first difi'usor becomes less diluted, than if the difiusor were first 60 washed with clean water. From the newly blown diffusor a strong black liquor is obtained at the beginning of the washing, which liquor by prior practice has been always sent to the soda house for regeneration of alkali, but according to the present invention such strong black liquor is used in the first place as supplemental liquor for a new charge in the digester. Such liquor should not have a lower specific gravity than 1.124. Instead of using, as such supplemental liquor, a black liquor having a specific gravity of 1.107, for instance, as has heretofore been customary, the strongest black liquoris thus used, which, in the case assumed, had a specific gravity of 1.149. In this manner a black liquor is obtained from the second boiling, which has a specific gravity of 1.160. This liquor is used in the first place as a supplemental liquor for charging a third boiler, which thus gives a still stronger waste liquor having a specific gravity of 1.170. This course is proceeded with until the desired concentration of the black liquor is obtained. Furthermore, by washing over from one difi'usor to another, as above described, the newly blown ditfusor is commenced at a higher concentration of the waste liquor than that hitherto used, namely, with black liquor having at the outset a specific gravity not lower than 1.090, the region of dilution becomes more limited during the washing, and accordingly the black liquor less diluted. In this manner it is possible for the regeneration to obtain a liquor having practically any deslred concentration. In practice, however, it is not 5 suitable to go beyond the point where the liquor remains liquid at 30 0., that is to say, it should not congeal at this temperature. That portion of the strong black liquor obtained in the manner above described which is not needed as supplemental liquor for the next digestion, is further evaporated, if rc quired, in suitable evaporation apparatus, or is directly combusted in suitable combustion apparatus.

Byusing white liquor having a higher percentage of alkali, such as, for instance, 180 active alkali per cu. m., only 7.8 cu. m. whlte liquor is needed in the case above assumed, instead of 11.7 cu. m., and for this reason it will thus be possible to replace 3.9 cu. m. water with concentrated black liquor, which Wlll further contribute to increasing the concentration ofthe black liquor This, however, it has previously not been possible to do in 1 practice, for the reason that the degreeof causticizing decreases at a high concentration of the soda solution to be causticized It is usual to prepare the white liquor in such manner that the evaporated soda is dissolved 120 in a melting state in water or in a weak white liquor obtained from washing the calcium carbonate precipitate obtained in the causticizing of the soda. Now, if this soda solution is made of a too high concentration it bc- 125 comes difiicult to causticize a high percentage of the sodium carbonate present in the solution. According to the present invention this difiiculty is avoided by dissolving the melting soda in a strong solution of white liquor, 1

With the use of the present method it using the'strongest waste liquor obtained from such washing in said difli'usors as supplemental liquorto the fresh digester liquor introduced into the digester for a subsequent digestion of a new charge, regenerating the remaining portion of the waste liquor to produce soda therefrom, dissolvin such soda in a strong N aOH-solution, an causticizing such solution to produce fresh digester liqnor.

BROR NATANAEL SEGERFELT.

tain a black liquor for the soda house having such specific gravity that only 4.5 cu. m. black liquor per 1000 kg. cellulose will have to be evaporated. a

I claim:

1. The method of producing cellulose which comprises digesting cellulosic material with digester liquor and afterwards Washing the cellulose produced in diffusors,evaporating the strongest waste liquor obtained from the diffusors from a previous boiling, and adding such evaporated waste liquor as supplemental liquor to the fresh digester liquor for obtaining the required quantity of liquid in the digester.

2. The method of producing cellulose which comprises digesting cellulosic material with digester liquor and afterwards washing the cellulose produced in difiusors, perform- 1 'ing the first washing in said difiusors with waste liquor having at the outset a specific gravity not less than 1.090, and adding the strongest waste liquor obtained from such washing in said difiusors as supplemental liquor to the fresh digester liquor for obtaining the required quantity of liquid in the digester.

3. The method of producing cellulose I which comprises digesting cellulosic material with digester liquor ina digester, concentrating the digester liquor in the digester during the digestion by removing steamv from the same, blowing the pulp and liquor to dif fusors when the digestion is completed, performing the first Washingin said difl'usors 4 with waste liquor having at the outset a specific gravity not less than 1.090, and using the strongest waste liquor first obtained from such washing in said diffusors as supplemental liquor to the fresh digester liquor introduced into the digester for a subsequent di- I gestion of a new charge.

4. The method of producing cellulose which comprises digesting cellulosic material with alkaline digester liquor in a digester, concentrating the digester liquor in the digester during the digestion by removing steam from the same, blowing the pulp and liquor diifusors when the digestion is completed, performing the first washing in said difiusors with waste liquor having at the outset a specific gravity'not less than 1.090, and 

